[ATF] add checks filter in policy

Allow studio to control which sets of validations to run.
Also added few more tests.

Bug: 150331000
Test: Manually tested + unit tests
Change-Id: I5dd81feaea5ff7dc0c7903612f0f1bc5c3cf22a2
(cherry picked from commit 9d6a3607f6ee3db03fe9fc2e686550078ca234f0)
4 files changed